This invention relates to microminiature inductive devices suitable for mounting on a mounting substrate such as a hybrid substrate or printed circuit board.
Prior art microminiature baluns, transformers and other inductive devices designed to be mounted to mounting substrates are fabricated with a small ceramic interconnect substrate that is attached to the mounting substrate with a conductive epoxy. This prior art epoxy attach method is illustrated in FIG. 1. Ceramic substrate 10 has metalized terminals 12 on the top surface interconnected to metalized terminals on the bottom surface (not shown) through metalized vias or plated through holes. The ceramic substrate 10 serves as an intermediate carrier wherein the windings 14 wrapped around inductor core 24 are soldered to the metalized terminals 12 of ceramic substrate 10 and the metalized terminals on the bottom surface are designed to mate with a matching terminal pattern 16 on the mounting substrate 18. The soldered wires are shown having soldered areas 20. When the ceramic substrate 10 is attached to the terminal pattern 16 with a conductive epoxy 22, two problems become apparent. The connection points to terminal pattern 16 are not visible from above since it is blocked by ceramic substrate 10 and the spreading of conductive epoxy 22 is not easy to control once the ceramic substrate has been placed on the mounting substrate 18. This prior art epoxy attach method may lead to shorting or an unreliable connection due to thermal stress. Further, the conductive epoxy has a relatively high impedance that is undesirable in many high current or high frequency applications.
Therefore, what is desired is an apparatus and method for joining a microminiature inductive device to a mounting substrate that is visible from above, does not have a tendency to short out or become unreliable due to thermal stress and does not use conductive epoxy.